The present invention relates to a thermoset polymaleimide resin composition. In particular, the present invention relates to a thermoset resin composition which exhibits excellent curing properties at low temperatures and produces hardened products having excellent heat resistance and mechanical properties.
Thermoset resins are widely used as adhesive, casting, painting, impregnating, laminating and molding compounds, in coating materials, insulating materials, composite structural materials and the like. However, thermoset resins have been recently used in various fields, and conventional thermoset resins are unsatisfactory in some environments of use and under some conditions of use. Conventional thermoset resins are particularly unsatisfactory for use at high temperatures, and there is thus a demand for development in this area.
Of thermoset resins, polyimide resins are one of the most excellent materials and are thus being developed in various aspects. For example, Japanese Patent Laid-Open No. 53319/1987 discloses a composition comprising a polymaleimide compound and a reactive oligomer having alkenyl ether groups at the terminals of its molecule. However, it is said that this resin composition is inferior to conventional resin such as epoxy based resin with respect to high curing temperature, long curing time, and workability involving these properties. This applies to the most typical composition comprising the combination of a bismaleimide and an aromatic amine or the combination of a bismaleimide, an aromatic amine and epoxy resin. There is therefore no resin composition exhibiting excellent heat resistance and mechanical physical properties, as well as excellent curing properties at low temperatures.
In consideration of the above-described situation, some of the inventors energetically investigated with a view to provide a polyimide resin composition having a low curing temperature and a short curing time, as well as exhibiting excellent heat resistance, heat stability and mechanical physical properties. As a result, they found and proposed that the formation of a composition containing maleimide compound, i.e., a thermoset resin composition comprising a maleimide compound and a compound of vinylbenzyl ether group bonded to an aromatic nucleus, which is represented by bisphenol divinylbenzyl ether, enables a reduction in the curing temperature and a significant reduction in the curing time, which are both curing properties (refer to Japanese Patent Laid-Open No. 65110/1989). However, such a composition has high viscosity and thus requires improvement.
As a result of further investigation, the inventors found that a thermoset polyimide resin composition having low working viscosity and excellent physical properties can be obtained by using a specific vinylbenzyl ether compound. This led to the achievement of the present invention.